Group III-V crystal and manufacturing method thereof

ABSTRACT

A method of manufacturing a group III-V crystal is made available by which good-quality group III-V crystals are easily obtained at low cost without causing cracks, even when using a variety of substrates. A method of manufacturing a group III-V crystal, characterized in including: a step of depositing a metal film ( 2 ) on a substrate ( 1 ); a step of heat-treating the metal film ( 2 ) in an atmosphere in which a patterning compound is present; and a step of growing a group III-V crystal ( 4 ) on the metal film after the heat treatment. Additionally, a method of manufacturing a group III-V crystal, characterized in including: a step of growing a group III-V compound buffer film on the metal film after the heat treatment; and a step of growing a group III-V crystal on the group III-V compound buffer film.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 of PCT/JP04/04811 filed on Apr. 1, 2004, whichclaims the benefit of Japan Patent Application No. 2003-129829, filedMay 8, 2003, the contents of which are hereby incorporated herein byreference in their entirety.

TECHNICAL FIELD

The present invention relates to crystals of group III-V compounds andto methods of their manufacture, and more particularly relates tomethods of manufacturing good-quality group III-V crystals withoutproducing cracks, even with the use of a variety of substrates.

BACKGROUND ART

Growing a crystal of a group III-V compound, such as GaN crystal, on asubstrate of a different material from the crystal material, such as asapphire substrate or a silicon (Si) substrate, causes stress betweenthe crystal and the substrate due to differences in properties such astheir crystal lattice constants and thermal expansion coefficients,leading to warps and cracks; thus, the process does not yield groupIII-V crystals of good quality.

In view of this problem, a method has been carried out for alleviatingthe stress between the crystals and the substrate by depositing a filmof a silicon oxide (such as SiO₂) on a sapphire substrate; patterningthe silicon oxide film is by a technique such as photolithography, andthereafter growing a group III-V crystal onto the patterned substrate.Such a method, however, is problematic in that it requires thepatterning of the silicon oxide film, which means the manufacturing costis high.

Another technique that has been proposed is one in which a GaN layer isgrown on a substrate such as sapphire by a metal organic chemical vapordeposition (MOCVD) technique, followed by the depositing of a metal filmthereon and performance of a heat treatment to form voids in the GaNlayer; thereafter, a GaN crystal is grown. (See Japanese Unexamined Pat.App. Pub. No. 2002-343728, for example.) Nevertheless, a problem ariseswith such a method because growing a GaN layer by MOCVD leads toextremely high manufacturing costs.

Still another technique that has been proposed is one in which a metalfilm is deposited on a sapphire or like substrate and thereafter a GaNcrystal is grown. (See Japanese Unexamined Pat. App. Pub. No.2002-284600, for example.) Such a method, however, is problematic inthat the qualities of the resulting GaN crystal are compromised becausethe GaN crystal is grown on a metal film that has a different latticeconstant from that of the GaN crystal.

DISCLOSURE OF INVENTION

An object of the present invention, brought about to resolve theforegoing problems, is to make available good-quality group III-Vcrystal that is obtained by a simple, low-cost manufacturing method, andto make available the manufacturing method.

In order to accomplish the foregoing object, a method of manufacturing agroup III-V compound according to the present invention is characterizedby comprising a step of depositing a metal film on a substrate; a stepof heat-treating the metal film under an atmosphere in which apatterning compound is present; and a step of growing a group III-Vcrystal on the metal film subsequent to the heat treatment.Additionally, the invention may be characterized in that the method mayfurther comprise, subsequent to the step of heat-treating, a step ofgrowing a group III-V compound buffer film on the metal film after theheat treatment; and a step of growing a group III-V crystal on the groupIII-V compound buffer film.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates one method of manufacturing a group III-V crystalaccording to the present invention;

FIG. 2 illustrates another method of manufacturing a group III-V crystalaccording to the present invention; and

FIG. 3A is a schematic diagram illustrating one representativeconfiguration of holes or grooves formed in a metal film, and FIG. 3B isa schematic diagram illustrating another representative configuration ofholes or grooves formed in a metal film.

BEST MODE FOR CARRYING OUT THE INVENTION EMBODIMENT 1

Referring to FIG. 1, one method of manufacturing a group III-V crystalaccording to the present invention is characterized in comprising a stepof depositing a metal film 2 on a substrate 1 as illustrated in FIG. 1A;a step, as represented in FIG. 1B, of heat-treating the metal film 2under an atmosphere in which a patterning compound is present; and astep, as represented in FIG. 1C, of growing a group III-V crystal 4 onthe metal film after the heat treatment.

Specifically, referring to FIGS. 1 and 3, a method of manufacturing agroup III-V crystal according to the present invention is carried outthrough the following steps. First, as illustrated in FIG. 1A, a metalfilm 2 is deposited on a substrate 1 using a technique such as vapordeposition or sputtering. Next, the metal film 2 is heat-treated underan atmosphere in which a patterning compound is present, whereby themetal film 2 becomes patterned in indefinite shapes as illustrated inFIG. 1B, forming holes or grooves 12 in a worm-eaten pattern, asillustrated in FIGS. 3A as well as 3B, exposing the substrate 1 at thebottoms of the holes or grooves 12. Subsequently, as illustrated in FIG.1C, a group III-V crystal 4 is grown, using a technique such as ahydride vapor phase epitaxy (HVPE), onto the metal film 2 in which theholes or grooves 12 in a worm-eaten pattern have been formed followingthe heat treatment.

Herein, each of FIGS. 3A and 3B schematically illustrates arepresentative configuration of holes or grooves in a worm-eaten patternthat are formed in the metal film 2 by heat-treating the metal film 2under an atmosphere in which a patterning compound is present. When thenumber of holes or grooves is small, a configuration such as that ofFIG. 3A tends to form, and as the number of holes or grooves increases,a configuration such as that of FIG. 3B tends to form.

By means of such a manufacturing method, a good-quality group III-Vcrystal 4 is grown because, as will be seen from FIG. 1, the group III-Vcrystal 4 can pick up information from the substrate 1 such as itscrystal lattice constant. Moreover, the formation in the metal film ofthe pattern of holes or grooves 12 in worm-eaten contours alleviates thestress between the group III-V crystal 4 and the metal film 2,preventing the group III-V crystal 4 from forming cracks. Furthermore,the manufacturing cost is reduced because the group III-V crystal can beproduced by a vapor phase epitaxy (VPE) technique such as the HVPEtechnique mentioned above, rather than by the high-cost MOCVD technique.

Referring to FIGS. 1 and 3, in the group III-V crystal manufacturingmethod according to the present invention, it is preferable that theholes or grooves formed in the metal film by heat-treating the metalfilm under an atmosphere in which a patterning compound is present havean average width W of 2 nm to 5000 nm and that the aperture fraction,which is the surface area that holes or grooves occupy, be 5% to 80% ofthe total area of the substrate. If the average width W of the holes orgrooves is less than 2 nm, the holes or grooves as formed do not reachthe substrate, making it difficult to read information from (that is,take on the characteristics of) the substrate. If on the other hand theaverage width W of the holes or grooves exceeds 5000 nm, it becomesdifficult to alleviate stress between the group III-V crystal and thesubstrate. Given these perspectives, it is further preferable that theaverage width W of the holes or grooves be from 5 nm to 1000 nm.Further, if the aperture fraction is less than 5% of the total area ofthe substrate, the smallness of the surface area in which the groupIII-V crystal is in contact with the substrate would be prohibitive ofthe growing III-V crystal reading information from the substrate. If onthe other hand the aperture fraction exceeds 80%, the excessively largeextent to which the metal film is absent would be prohibitive ofalleviating stress between the group III-V crystal and the substrate.Given these perspectives, it is further preferable that the aperturefraction be 10% to 50% of the total area of the substrate. Herein,aperture fraction is defined as the percentage of surface area that theholes or grooves occupy with respect to the total area of the substrate,according to the following equation (1):

$\begin{matrix}{{{Aperture}\mspace{14mu}{fraction}\mspace{14mu}(\%)} = {\frac{\left( {{holes}\mspace{14mu}{or}\mspace{14mu}{grooves}\mspace{14mu}{occupying}\mspace{14mu}{area}} \right)}{\left( {{substrate}\mspace{14mu}{total}\mspace{14mu}{surface}\mspace{14mu}{area}} \right)} \times 100}} & (1)\end{matrix}$

As for the substrate herein, a wide variety of substrates may be used,whether the same kind as or a different kind from the group III-Vcrystal to be grown, as long as its use does not conflict with theobject of the present invention. For example, silicon, sapphire, SiC,ZrB₂, or group III-V compounds are preferable because the latticeconstants of crystals of these compounds are similar to the latticeconstant of the group III-V crystals, and thus, good-quality crystalsare readily produced. It should be noted that the group III-V compoundused for the substrate need not be the same compound as the group III-Vcrystal that is to be grown thereon.

Although there are no restrictions on the metal film, a metal filmcontaining titanium (Ti) or vanadium (V), including such metals andalloys as Ti, Ti—Al, V, and V—Al, is preferable from the viewpoint ofreadiness for patterning.

Although not particularly limited, the thickness of the metal film ispreferably 10 nm to 1000 nm. A film thickness of less than 10 nm isprohibitive of causing the metal film to stay in the patterningoperation, while the thickness exceeding 1000 nm is prohibitive ofexposing the substrate in the patterning operation. In light of thesefactors, it is preferable that the thickness of the metal film be 30 nmto 500 nm.

A compound that patterns the metal film means a compound, preferableexamples of which include ammonia (NH₃) and nitrogen (N₂), that when ametal film is heat-treated under an atmosphere in which the compound ispresent patterns into indefinite shapes holes or grooves in worm-eatencontours in the metal film.

Preferable heat-treating conditions for heat-treating of metal film inan atmosphere in which a patterning compound is present are temperaturesof 800° C. to 1200° C. for a duration of 0.5 minutes to 20 minutes. Ifthe heat-treatment temperature is less than 800° C. or theheat-treatment time is less than 0.5 minutes, insufficient patterning ofthe metal film results; if the heat-treatment temperature exceeds 1200°C. or the heat-treatment time exceeds 20 minutes, the metal film ispatterned excessively. In light of these factors, it is preferable thatthe heat-treatment temperature be 900° C. to 1100° C. and theheat-treatment time 0.5 minutes to 10 minutes.

The simple and low-cost manufacturing method described above yieldsgood-quality group III-V crystals. Furthermore, in cases in which theIII-V crystals in the foregoing are Ga_(x)Al_(y)In_(1-x-y) (0≦x≦1 and0≦y≦1), because at present there is no other particularly serviceablemanufacturing method for such crystals, the method proves to be aninvaluable manufacturing technique.

EMBODIMENT 2

Referring to FIG. 2, another method of manufacturing a group III-Vcrystal according to the present invention is characterized incomprising: a step of depositing a metal film 2 on a substrate 1 asillustrated in FIG. 2A; a step, as represented in FIG. 2B, ofheat-treating the metal film in an atmosphere in which a patterningcompound is present; a step, as represented in FIG. 2C, of growing agroup III-V compound buffer film 3 on the metal film 2 after the heattreatment; and a step, as represented in FIG. 2D, of growing a groupIII-V crystal 4 on the group III-V compound buffer film 3.

Specifically, referring to FIGS. 2 and 3, another method ofmanufacturing a group III-V crystal according to the present inventionis carried out through the following steps. First, as illustrated inFIG. 2A, a metal film 2 is deposited on a substrate 1 using such atechnique as vapor deposition or sputtering. Next, the metal film 2 isheat-treated in an atmosphere in which a patterning compound is present,whereby the metal film 2 is patterned in indefinite shapes asillustrated in FIG. 2B, forming holes or grooves 12 in worm-eatencontours, as illustrated in FIG. 3A as well as 3B, so that the substrate1 is exposed in the bottoms of the holes or grooves 12.

Next, using, for example, an HVPE technique a group III-V compoundbuffer film 3 as illustrated in FIG. 2C is grown onto thepost-heat-treated metal film 2 in which the holes or grooves 12 inworm-eaten contours are formed. Herein, the term “a group III-V compoundbuffer film” 3 refers to an amorphous film of the group III-V compoundthat is grown at a lower temperature than that for growing the crystal.Subsequently, as illustrated in FIG. 2D, a group III-V crystal 4 isgrown on the group III-V compound buffer film 3, using, for example, anHVPE technique.

In Embodiment 2, described above, the formation onto the metal film 2 inwhich holes or grooves in a worm-eaten pattern have been formed makes itpossible to alleviate the stress between the substrate 1 and the groupIII-V crystal 4 that is later formed on the group III-V compound bufferfilm 3. Moreover, because the group III-V crystal 4 in growing picks upinformation not from the substrate 1 but from the amorphous III-V film,even better-quality III-V crystal—crystal that has not taken inunnecessary crystalline information—is produced.

EXAMPLES

Embodiments 1 and 2 described above are further detailed based onspecific examples.

Example 1

Reference is made to FIG. 1. Based on Embodiment 1, by a vapordeposition technique a 30 nm-thick metallic Ti film was deposited as ametal film 2 on a substrate 1, as illustrated in FIG. 1A, using asapphire base as the substrate 1. Next, as represented in FIG. 1B themetal film 2 was heat-treated within a NH₃ atmosphere at 1000° C. for0.5 minutes. The surface of the metal film 2 after its temperature waslowered was observed with a scanning electron microscope (SEM). Holes orgrooves in a worm-eaten pattern as shown in FIG. 3A were found; theaverage width W of the holes or grooves was 8 nm and the aperturefraction was 12%. In addition, a group III-V crystal 4 as illustrated inFIG. 1C was grown at 1000° C. for a 5-hour duration by an HVPE techniqueusing Ga and NH₃ as source materials, resulting in a crystal free ofcracks. The resulting crystal was found to be a good-quality GaN crystalby an XRD measurement, with its full width at half-maximum (FWHM) in theXRD being 120 arsec. The results are set forth in Table I.

Examples 2 to 12

With the test conditions set out in Table I, group III-V crystals weregrown by the same procedure as in Example 1. The results are summarizedin Table I.

TABLE I Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex.11 Ex. 12 Substrate type Sapphire Sapphire GaAs Sapphire Si AlN ZrB₂ GaNSiC Sapphire Sapphire Si Metal film Class Ti Ti Ti Ti Ti Ti Ti Ti (90) VV Ti Ti (Composition: Al (10) mole %) Film thick- 30 200 200 200 200 500200 300 200 200 200 200 ness(nm) Heat treat- ment Atmosphere NH₃ NH₃ NH₃NH₃ NH₃ N₂ NH₃ (40) NH₃ NH₃ NH₃ NH₃ NH₃ (Composition: H₂ (60) mole %)Temp. (° C.) 1000 800 1000 1000 1100 1200 1000 1000 1000 1000 1000 1100Duration (min.) 0.5 10 6 3 3 10 3 3 3 2 3 3 Hole/groove width 8 10 11031 280 900 32 26 29 18 31 280 width (nm) Aperture 12 25 34 22 45 75 2218 11 8 22 38 fraction (%) Crystal growth Source material 1 Ga Ga Ga GaGa Ga Ga Ga Ga Ga (80) Al Ga (70) (Composition: Al (10) Al (30) mole %)In (10) Source material 2 NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ NH₃NH₃ (Composition: mole %) Temp. (° C.) 1000 1100 1000 1000 1100 10001000 1000 1100 1000 1000 1100 Duration (hrs.) 5 5 5 5 5 5 5 5 5 5 5 5Cracking None None None None None None None None None None None Noneincidents Crystal GaN GaN GaN GaN GaN GaN GaN GaN GaN Ga_(0.8) AlNGa_(0.7) composition Al_(0.1) Al_(0.3)N (XRD-iden- In_(0.1)N tified) XRDFWHM 120 120 103 110 105 108 118 135 138 150 115 97 (arsec)

Example 13

Reference is made to FIG. 2. Based on Embodiment 2, by a vapordeposition technique a 200 nm-thick metallic Ti film was deposited as ametal film 2 on a substrate 1, as illustrated in FIG. 2A, using asapphire base as the substrate 1. Next, as represented in FIG. 2B themetal film 2 was heat-treated in a NH₃ atmosphere at 1000° C. for 3minutes. the surface of the metal film 2 after its temperature waslowered was observed with an SEM. Holes or grooves in a worm-eatenpattern as shown in FIG. 3A were found; the average width W of the holesor grooves was 31 nm and the aperture fraction was 22%. Next, a groupIII-V compound buffer film 3 as illustrated in FIG. 2C was grown at 500°C. for a 0.5-hour duration. Then, a group III-V crystal 4 as illustratedin FIG. 2D was grown at 1000° C. for a 5-hour duration by an HVPEtechnique using Ga and NH₃ as source materials, resulting in a crystalfree of cracks. The resulting crystal was found to be a good-quality GaNcrystal by an XRD measurement, with its FWHM in the XRD being 80 arsec.The results are set forth in Table I.

Examples 14 to 20

With the test conditions set out in Table II, group III-V crystals weregrown in the same procedure as in Example 13. The results are summarizedin Table II.

TABLE II Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18 Ex. 19 Ex. 20Substrate type Sapphire Si GaAs AlN GaN SiC Sapphire Si Metal Film ClassTi Ti Ti Ti Ti (90) V Ti Ti (Comp.: mole %) Al (10) Film thick- 200 200200 500 300 200 200 200 ness (nm) Heat treat- ment Atmosphere NH₃ NH₃NH₃ N₂ NH₃ NH₃ NH₃ NH₃ (Comp.: mole %) Temp. (° C.) 1000 1100 1000 12001000 1000 1000 1100 Duration (min.) 3 3 6 10 3 3 3 3 Hole/groove 31 280110 900 26 29 31 280 width (nm) Aperture frac- 22 45 34 75 18 11 22 38tion (%) Buffer film growth Source material 1 Ga Ga Al Ga Ga Ga Al Ga(70) (Comp.: mole %) Al (30) Source material 2 NH₃ NH₃ NH₃ NH₃ NH₃ NH₃NH₃ NH₃ (Comp.: mole %) Temp. (° C.) 500 500 500 500 500 500 500 500Duration (hrs.) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Crystal growth Sourcematerial 1 Ga Ga Ga Ga Ga Ga Al Ga (70) (Comp.: mole %) Al (30) Sourcematerial 2 NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ (Comp.: mole %) Temp. (° C.)1000 1100 1000 1000 1000 1000 1000 1100 Duration (hrs.) 5 5 5 5 5 5 5 5Cracking incidents None None None None None None None None Crystalcomposition GaN GaN GaN GaN GaN GaN AlN Ga_(0.7) (XRD-identified)Al_(0.3)N XRD FWHM 80 65 72 85 88 92 90 78 (arsec)

As is evident from Tables I and II, good-quality group III-V crystalsthat are free from cracks were obtained in all of the examples.Furthermore, it will be understood from comparisons, for example,between Examples 4 and 13, and between Examples 11 and 19, that theFWHMs of the crystals in the XRD analysis were reduced from 110 arsec to80 arsec and from 115 arsec to 90 arsec, respectively, and that growingthe buffer film prior to growing a group III-V crystal improved thequality of the crystals further.

It should be understood that the presently disclosed embodiments andexamples are in all respects illustrative and not limiting. The scope ofthe present invention is set forth not by the foregoing description butby the scope of the patent claims, and is intended to include meaningsequivalent to the scope of the patent claims and all modificationswithin the scope.

INDUSTRIAL APPLICABILITY

As described in the foregoing, in accordance with the present invention,the provision of a step of depositing a metal film on a substrate, astep of heat-treating the metal film in an atmosphere in which apatterning compound is present, and a step of growing a group III-Vcrystal on the metal film after the heat treatment, yields good-qualitygroup III-V crystals without causing cracks, using a simple and low-costmanufacturing method.

1. A method of manufacturing a crystal of a group III-V compound, themethod comprising: a deposition step of depositing a metal film on asubstrate; a heat-treatment step of heat-treating the metal film underan atmosphere in which a metal-film patterning compound is present sothat the metal film becomes patterned with a plurality of grooves havingan indefinite shape, the grooves having an average width of 2 nm to 5000nm, the metal film having an aperture fraction of 5% to 80%, theaperture fraction being the percentage of the surface area that thegrooves occupy with respect to the substrate total surface area; and agrowth step of growing a group III-V crystal on the post-heat-treatedmetal film.
 2. A method of manufacturing a crystal of a group III-Vcompound, the method comprising: a deposition step of depositing a metalfilm on a substrate; a heat-treatment step of heat-treating the metalfilm under an atmosphere in which a metal-film patterning compound ispresent so that the metal film becomes patterned with a plurality ofgrooves having an indefinite shape, the grooves having an average widthof 2 nm to 5000 nm, the metal film having an aperture fraction of 5% to80%, the aperture fraction being the percentage of the surface area thatthe grooves occupy with respect to the substrate total surface area; afirst growth step of growing a group III-V compound buffer film on thepost-heat-treated metal film; and a second growth step of growing agroup III-V crystal on the group III-V compound buffer film.
 3. A groupIII-V crystal manufacturing method as set forth in claim 1,characterized in that the substrate is silicon, sapphire, SiC, ZrB₂, ora group III-V compound.
 4. A group III-V crystal manufacturing method asset forth in claim 1, characterized in that the metal film containstitanium or vanadium.
 5. A group III-V crystal manufacturing method asset forth in claim 1, wherein the method renders the thickness of themetal film to be 10 nm to 100 nm.
 6. A group III-V crystal manufacturingmethod as set forth in claim 1, characterized in that the heat treatmentis carried out at 800° C. to 1200° C. for 0.5 minutes to 20 minutes. 7.A group III-V compound crystal manufactured by a group III-V crystalmanufacturing method as set forth in claim
 1. 8. A group III-V compoundcrystal as set forth in claim 7, wherein the group III-V crystal isGa_(x)Al_(y)In_(1-x-y) (0≦x≦1 and 0≦y≦1).
 9. A group III-V crystalmanufacturing method as set forth in claim 2, characterized in that thesubstrate is silicon, sapphire, SiC, ZrB₂, or a group III-V compound.10. A group III-V crystal manufacturing method as set forth in claim 2,characterized in that the metal film contains titanium or vanadium. 11.A group III-V crystal manufacturing method as set forth in claim 2,wherein the method renders the thickness of the metal film to be 10 nmto 100 nm.
 12. A group III-V crystal manufacturing method as set forthin claim 2, characterized in that the heat treatment is carried out at800° C. to 1200° C. for 0.5 minutes to 20 minutes.
 13. A group III-Vcompound crystal manufactured by a group III-V crystal manufacturingmethod as set forth in claim
 2. 14. A group III-V compound crystal asset forth in claim 13, wherein the group III-V crystal isGa_(x)Al_(y)In_(1-x-y) (0≦x≦1 and 0≦y≦1).